In a pulp dryer, a web formed of pulp, i.e. a pulp web, is conveyed along a multi-layered path by floating it on an air cushion formed by blow nozzles. The blow nozzles are arranged in several superimposed, generally horizontal nozzle levels almost having the length of the pulp dryer. The pulp web is typically introduced in the pulp dryer through its first end. Then the pulp web is conveyed along the uppermost nozzle level of the pulp dryer to the second end of the device. At its ends, the device typically comprises turn rolls, over which the pulp web is turned each time to the next lower nozzle level. When the pulp web has been conveyed to the lowest nozzle level of the pulp dryer, the pulp web is removed from the pulp dryer, typically through the second end of the pulp dryer. A pulp dryer typically comprises 15-30 nozzle levels. The gas blown from the blow nozzles is typically hot air, the blow air generally having a temperature in the range of 120-170° C. When reaching the pulp dryer, the pulp web typically has a dry solids content of 48-54%. The dry solids content of the pulp web leaving the pulp dryer is typically 85-95%, most typically approximately 90%. The pulp web typically has a width of 3-9 m. The pulp web is typically conveyed at a speed of 140-220 m/min in the pulp dryer.
The pulp web may break within the dryer for various reasons. In such a situation, the feed of a new pulp web into the pulp dryer is interrupted. However, in the case of a web break, there will typically still remain a large amount of pulp web in the pulp dryer, which web needs to be removed from the device before the production is restarted.
In the case of a web break, the pulp web is currently removed from the dryer by means of extraction devices fixed to maintenance platforms moving vertically at the first end and the second end of the pulp dryer. An extraction device is fixed to that edge of the maintenance platform which is directed away from the dryer, typically at least partly outside the railings of the maintenance platform. The extraction device comprises two horizontal rolls transverse to the direction of movement of the pulp web. The rolls are arranged against each other so that a nip of the extraction device is formed between them. The rolls are arranged to be rotated by machine force. The pulp web needs to be pulled by muscular force from the inside of the dryer to the nip of the extraction device, whereafter the pulp web can be extracted by machine force with the aid of the rolls and further guided to a pulper. The distance over which the pulp web needs to be transferred by manpower is typically 2-3 metres. After a web break, the wet pulp web remains on the nozzle levels and the pulp web will typically have time to dry at least partly before cleaning operations are started. Consequently, friction between the nozzle levels and the web will impede cleaning operations, even though with the aid of nozzle blowing the situation can be made somewhat easier. Extraction of the pulp web from the pulp dryer requires strong force. The operation usually requires 2 or 3 operators.
International patent publication WO 02/101143 discloses a solution, in which a wheel is used for pressing a broken pulp web against a rotating turn roll. In this manner, a pulling nip is formed between the wheel and the turn roll, due to which the pulp web will start moving. In the solution presented either manpower is needed or the device requires installations in the inner parts of the pulp dryer. If an extraction device fixed to the maintenance platform is used in connection with the solution presented in the publication, the device is fixed to that edge of the maintenance platform which is directed away from the pulp dryer. In this case, the broken pulp web needs to be pulled over the maintenance platform such that working on the maintenance platform is difficult or even impossible. The pulp web can also foul the maintenance platform.